Autodepositable adhesive

ABSTRACT

A method for bonding two substrates that includes applying an autodepositable adhesive to one of the substrates and then bonding the substrates together. This method is especially useful for bonding elastomers to metals. According to a first embodiment, the autodepositable adhesive is a one coat adhesive having a low pH (approximately 1-3) and including (A) a flexibilizer or film-former, (B) optionally, an aqueous dispersion of a phenolic resin that includes water and a reaction product of a phenolic resin precursor, a modifying agent and, optionally, a multi-hydroxy phenolic compound wherein the modifying agent includes at least one functional moiety that enables the modifying agent to react with the phenolic resin precursor and at least one ionic moiety, and (C) an acid. According to a second embodiment, the autodepositable adhesive is a covercoat adhesive that includes a flexibilizer or film-former that is a latex that coagulates when exposed to metallic ions generated from the metallic substrate upon which the covercoat is applied. The covercoat preferably also includes a crosslinker as described above in connection with the one coat embodiment.

[0001] This application claims benefit of U.S. Provisional ApplicationNo. 60/116,767, filed Jan. 22, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an autodepositable adhesive,particularly an adhesive for bonding an elastomeric material to ametallic material.

[0003] It is generally known that the corrosion resistance of metalsubstrates can be improved by coating the substrate with anautodeposition composition that generally comprise an aqueous solutionof an acid, an oxidizing agent and a dispersed resin. Immersion of ametallic surface in an autodeposition composition produces what is saidto be a self-limiting protective coating on a metal substrate. Thegeneral principles and advantages of autodeposition are explained in amultitude of patents assigned to Parker Amchem and/or Henkel (see, forexample, U.S. Pat. Nos. 4,414,350; 4,994,521; 5,427,863; 5,061,523 and5,500,460). However, to the best of the inventors' knowledge theseautodeposition compositions have not been successfully used as one coatadhesives or covercoat adhesives.

[0004] Elastomer-to-metal bonding is subjected to severe environmentalconditions in many industrial and automotive assemblies. For example,many engine mounting assemblies that employ elastomer-to-metal bondingcontain fluids in order to assist in damping of vibration of the engine.These fluid-filled engine mounting devices are being increasinglyexposed to high temperatures such that the elastomer-to-metal adhesivebonds within the mounts are being exposed to very high temperature fluidenvironments. Many elastomer-to-metal assemblies, particularly thoseutilized in automobile applications, are routinely exposed to materialsthat contain corrosive salts or other corrosive materials that may actto degrade the elastomer-to-metal adhesive bond.

[0005] In light of the increasing regulations regarding volatile organiccompounds (VOC), the use of traditional solvent-borne adhesives isbecoming more problematic. Consequently, there is significant ongoingwork to develop water-borne replacements. Current aqueous adhesivessuffer from user drawbacks. Application of an adhesive by dipping theadherend in a bath of the adhesive is frequently preferred by the userdue to its simplicity. However, dipping of aqueous adhesives leads toproblems with controlling the film thickness and dripping.

SUMMARY OF THE INVENTION

[0006] According to the present invention there is provided a method forbonding two substrates comprising applying an autodepositable adhesiveto one of the substrates and then bonding the substrates together. Thismethod is especially useful for bonding elastomers to metals.

[0007] According to a first embodiment, the autodepositable adhesive isa one coat adhesive having a low pH (approximately 1-3) and including(A) a flexibilizer or film-former, (B) optionally, an aqueous dispersionof a phenolic resin that includes water and a reaction product of aphenolic resin precursor, a modifying agent and, optionally, amulti-hydroxy phenolic compound wherein the modifying agent includes atleast one functional moiety that enables the modifying agent to reactwith the phenolic resin precursor and at least one ionic moiety, and (C)an acid. According to a more particular embodiment of a one coatadhesive, the adhesive further includes a control agent that improvesthe uniformity of the film thickness formed by the adhesive. Organicnitro compounds are the preferred control agents. According to anotherparticular embodiment of a one coat adhesive, the adhesive furtherincludes a crosslinker that improves the adhesive performance. Thecrosslinker can be an aromatic nitroso compound or aromatic nitrosocompound precursor.

[0008] According to a second embodiment, the autodepositable adhesive isa covercoat adhesive that includes a flexibilizer or film-former that isa latex that coagulates when exposed to metallic ions generated from themetallic substrate upon which the covercoat is applied. The covercoatpreferably also includes a crosslinker as described above in connectionwith the one coat embodiment.

[0009] The one coat autodepositable adhesive can be autodeposited on ametal substrate and then an elastomeric substrate is contacted to themetal substrate to effect bonding of the metal substrate to theelastomeric substrate. The covercoat autodepositable adhesive preferablyis applied onto a metal substrate that has been previously treated orcoated with an autodepositable metal treatment composition or primer.The autodepositable metal treatment or primer provides the acidicenvironment that generates metal ions thereby activating theautodeposition characteristic of the autodepositable covercoat adhesive.

[0010] An autodepositable adhesive provides for easier film thicknesscontrol, increased film thickness uniformity and substantiallyeliminates dripping. The autodepositable adhesive also is substantiallyfree of volatile organic compounds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Unless otherwise indicated, description of components in chemicalnomenclature refers to the components at the time of addition to anycombination specified in the description, but does not necessarilypreclude chemical interactions among the components of a mixture oncemixed.

[0012] Certain terms used in this document are defined below.

[0013] “Phenolic compound” means a compound that includes at least onehydroxy functional group attached to a carbon atom of an aromatic ring.Illustrative phenolic compounds include unsubstituted phenol per se,substituted phenols such as alkylated phenols and multi-hydroxy phenols,and hydroxy-substituted multi-ring aromatics. Illustrative alkylatedphenols include methylphenol (also known as cresol), dimethylphenol(also known as xylenol), 2-ethylphenol, pentylphenol and tert-butylphenol. “Multi-hydroxy phenolic compound” means a compound that includesmore than one hydroxy group on each aromatic ring. Illustrativemulti-hydroxy phenols include 1,3-benzenediol (also known asresorcinol), 1,2-benzenediol (also known as pyrocatechol),1,4-benzenediol (also known as hydroquinone), 1,2,3-benzenetriol (alsoknown as pyrogallol), 1,3,5-benzenetriol and4-tert-butyl-1,2-benzenediol (also known as tert-butyl catechol).Illustrative hydroxy-substituted multi-ring aromatics include4,4′-isopropylidenebisphenol (also known as bisphenol A),4,4′methylidenebisphenol (also known as bisphenol F) and naphthol.

[0014] “Aldehyde compound” means a compound having the generic formulaRCHO. Illustrative aldehyde compounds include formaldehyde,acetaldehyde, propionaldehyde, n-butylaldehyde, n-valeraldehyde,caproaldehyde, heptaldehyde and other straight-chain aldehydes having upto 8 carbon atoms, as well as compounds that decompose to formaldehydesuch as paraformaldehyde, trioxane, furfural, hexamethylenetriamine,acetals that liberate formaldehyde on heating, and benzaldehyde.

[0015] “Phenolic resin” generally means the reaction product of aphenolic compound with an aldehyde compound. The molar ratio of thealdehyde compound (for example, formaldehyde) reacted with the phenoliccompound is referred to herein as the “F/P ratio”. The F/P ratio iscalculated on a per hydroxy-substituted aromatic ring basis.

[0016] “Phenolic resin precursor” means an unmodified or conventionalphenolic resin that is reacted with the aromatic modifying agent toproduce the phenolic resin that is dispersed in an aqueous phase.

[0017] As described above, there are two embodiments of theinvention—one coat and covercoat. “One coat adhesive” means acomposition that by itself adheres together two substrate surfaceswithout the need for a primer. For example, a one coat adhesiveaccording to the invention can be directly applied to a metal surfacethat has been simply conventionally treated or converted such as byphosphatizing, degreasing/descaling or grit blasting. “Covercoatadhesive” means a composition that is applied over a primer orautodepositable metal treatment composition to enable the bonding of twosubstrate surfaces.

[0018] The flexibilizer or film-former can be any ingredient that formsa film and/or any material that contributes flexibility and/or toughnessto the film formed from the composition. The toughness provided by theflexibilizer provides fracture resistance to the film. The flexibilizershould be non-glassy at ambient temperature and an aqueous emulsionlatex or aqueous dispersion that is compatible with the other componentsof the adhesive. The flexibilizer preferably is formulated into theadhesive composition in the form of an aqueous emulsion latex or aqueousdispersion.

[0019] In the covercoat adhesive embodiment of the invention theflexibilizer should destabilize by metal ions from the substrate so thatit can coagulate when applied to a metal substrate that has beenpreviously activated through application of an acidic metal treatment orprimer.

[0020] Suitable flexibilizers include aqueous latices, emulsions ordispersions of (poly)butadiene, neoprene, styrene-butadiene rubber,acrylonitrile-butadiene rubber (also known as nitrile rubber),halogenated polyolefin, acrylic polymer, urethane polymer,ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymerrubber, styrene-acrylic copolymer, polyamide, poly(vinyl acetate) andthe like. Halogenated polyolefins, nitrile rubbers and styrene-acryliccopolymers are preferred.

[0021] A suitable styrene-acrylic polymer latex is commerciallyavailable from Goodyear Tire & Rubber under the trade designationPLIOTEC and described, for example, in U.S. Pat. Nos. 4,968,741;5,122,566 and 5,616,635. According to U.S. Pat. No. 5,616,635, such acopolymer latex is made from 45-85 weight percent vinyl aromaticmonomers, 15-50 weight percent of at least one alkyl acrylate monomerand 1-6 weight percent unsaturated carbonyl compound. Styrene is thepreferred vinyl aromatic monomer, butyl acrylate is the preferredacrylate monomer and acrylic acid and methacrylic acid are the preferredunsaturated carbonyl compound. The mixture for making the latex alsoincludes at least one phosphate ester surfactant, at least onewater-insoluble nonionic surface active agent and at least one freeradical initiator.

[0022] If nitrile rubber is the flexibilizer, it is preferably mixedinto the composition as an emulsion latex. It is known in the art thatnitrile rubber emulsion latices are generally made from at least onemonomer of acrylonitrile or an alkyl derivative thereof and at least onemonomer of a conjugated diene, preferably butadiene. According to U.S.Pat. No. 4,920,176 the acrylonitrile or alkyl derivative monomer shouldbe present in an amount of 0 or 1 to 50 percent by weight based on thetotal weight of the monomers. The conjugated diene monomer should bepresent in an amount of 50 percent to 99 percent by weight based on thetotal weight of the monomers. The nitrile rubbers can also optionallyinclude various co-monomers such as acrylic acid or various estersthereof, dicarboxylic acids or combinations thereof. The polymerizationof the monomers typically is initiated via free radical catalysts.Anionic surfactants typically are also added. A suitable nitrile rubberlatex is available from B.F. Goodrich under the trade designation HYCAR.

[0023] Representative halogenated polyolefins include chlorinatednatural rubber, chlorine- and bromine-containing synthetic rubbersincluding polychloroprene, chlorinated polychloroprene, chlorinatedpolybutadiene, hexachloropentadiene, butadiene/halogenated cyclicconjugated diene adducts, chlorinated butadiene styrene copolymers,chlorinated ethylene propylene copolymers andethylene/propylene/non-conjugated diene terpolymers, chlorinatedpolyethylene, chlorosulfonated polyethylene,poly(2,3-dichloro-1,3-butadiene), brominatedpoly(2,3-dichloro-1,3-butadiene), copolymers of α-haloacrylonitriles and2,3-dichloro-1,3-butadiene, chlorinated poly(vinyl chloride) and thelike including mixtures of such halogen-containing elastomers.

[0024] Latices of the halogenated polyolefin can be prepared accordingto methods known in the art such as by dissolving the halogenatedpolyolefin in a solvent and adding a surfactant to the resultingsolution. Water can then be added to the solution under high shear toemulsify the polymer. The solvent is then stripped to obtain a latex.The latex can also be prepared by emulsion polymerization of thehalogenated ethylenically unsaturated monomers.

[0025] Butadiene latices are particularly preferred as the film-formeror flexibilizer. Methods for making butadiene latices are well known andare described, for example, in U.S. Pat. Nos. 4,054,547 and 3,920,600,both incorporated herein by reference. In addition, U.S. Pat. Nos.5,200,459; 5,300,555; and 5,496,884 disclose emulsion polymerization ofbutadiene monomers in the presence of polyvinyl alcohol and a co-solventsuch as an organic alcohol or a glycol.

[0026] The butadiene monomers useful for preparing the butadiene polymerlatex can essentially be any monomer containing conjugated unsaturation.Typical monomers include 2,3-dichloro-1,3-butadiene; 1,3-butadiene;2,3-dibromo-1,3-butadiene isoprene; isoprene; 2,3-dimethylbutadiene;chloroprene; bromoprene; 2,3-dibromo-1,3-butadiene;1,1,2-trichlorobutadiene; cyanoprene; hexachlorobutadiene; andcombinations thereof. It is particularly preferred to use2,3-dichloro-1,3-butadiene since a polymer that contains as its majorportion 2,3-dichloro-1,3-butadiene monomer units has been found to beparticularly useful in adhesive applications due to the excellentbonding ability and barrier properties of the2,3-dichloro-1,3-butadiene-based polymers. As described above, anespecially preferred embodiment of the present invention is one whereinthe butadiene polymer includes at least 60 weight percent, preferably atleast 70 weight percent, 2,3-dichloro-1,3-butadiene monomer units.

[0027] The butadiene monomer can be copolymerized with other monomers.Such copolymerizable monomers include α-haloacrylonitriles such asα-bromoacrylonitrile and α-chloroacrylonitrile; α,β-unsaturatedcarboxylic acids such as acrylic, methacrylic, 2-ethylacrylic,2-propylacrylic, 2-butylacrylic and itaconic acids;alkyl-2-haloacrylates such as ethyl-2-chloroacrylate andethyl-2-bromoacrylate; α-bromovinylketone; vinylidene chloride; vinyltoluenes; vinylnaphthalenes; vinyl ethers, esters and ketones such asmethyl vinyl ether, vinyl acetate and methyl vinyl ketone; estersamides, and nitriles of acrylic and methacrylic acids such as ethylacrylate, methyl methacrylate, glycidyl acrylate, methacrylamide andacrylonitrile; and combinations of such monomers. The copolymerizablemonomers, if utilized, are preferably α-haloacrylonitrile and/orα,β-unsaturated carboxylic acids. The copolymerizable monomers may beutilized in an amount of 0.1 to 30 weight percent, based on the weightof the total monomers utilized to form the butadiene polymer.

[0028] In carrying out the emulsion polymerization to produce the latexother optional ingredients may be employed during the polymerizationprocess. For example, conventional anionic and/or nonionic surfactantsmay be utilized in order to aid in the formation of the latex. Typicalanionic surfactants include carboxylates such as fatty acid soaps fromlauric, stearic, and oleic acid; acyl derivatives of sarcosine such asmethyl glycine; sulfates such as sodium lauryl sulfate; sulfated naturaloils and esters such as Turkey Red Oil; alkyl aryl polyether sulfates;alkali alkyl sulfates; ethoxylated aryl sulfonic acid salts; alkyl arylpolyether sulfonates; isopropyl naphthalene sulfonates; sulfosuccinates;phosphate esters such as short chain fatty alcohol partial esters ofcomplex phosphates; and orthophosphate esters of polyethoxylated fattyalcohols. Typical nonionic surfactants include ethoxylated (ethyleneoxide) derivatives such as ethoxylated alkyl aryl derivatives; mono- andpolyhydric alcohols; ethylene oxide/propylene oxide block copolymers;esters such as glyceryl monostearate; products of the dehydration ofsorbitol such as sorbitan monostearate and polyethylene oxide sorbitanmonolaurate; amines; lauric acid; and isopropenyl halide. A conventionalsurfactant, if utilized, is employed in an amount of 0.01 to 5 parts,preferably 0.1 to 2 parts, per 100 parts by weight of total monomersutilized to form the butadiene polymer.

[0029] In the case of dichlorobutadiene homopolymers, anionicsurfactants are particularly useful. Such anionic surfactants includealkyl sulfonates and alkyl aryl sulfonates (commercially available fromStepan under the trade designation POLYSTEP) and sulfonic acids or saltsof alkylated diphenyl oxide (for example, didodecyl diphenyleneoxidedisulfonate or dihexyl diphenyloxide disulfonate commercially availablefrom Dow Chemical Co. under the trade designation DOWFAX).

[0030] Chain transfer agents may also be employed during emulsionpolymerization in order to control the molecular weight of the butadienepolymer and to modify the physical properties of the resultant polymeras is known in the art. Any of the conventional organicsulfur-containing chain transfer agents may be utilized such as alkylmercaptans and dialkyl xanthogen disulfides.

[0031] The emulsion polymerization is typically triggered by a freeradical initiator. Illustrative free radical initiators includeconventional redox systems, peroxide systems, azo derivatives andhydroperoxide systems. The use of a redox system is preferred andexamples of such systems include ammonium persulfate/sodiummetabisulfite, ferric sulfate/ascorbic acid/hydroperoxide andtributylborane/hydroperoxide, with ammonium persulfate/sodiummetabisulfite being most preferred.

[0032] The emulsion polymerization is typically carried out at atemperature of 10°-90° C., preferably 40°-60° C. Monomer conversionusually ranges from 70-100, preferably 80-100, percent. The laticespreferably have a solids content of 10 to 70, more preferably 30 to 60,percent; a viscosity between 50 and 10,000 centipoise at 25° C.; and aparticle size between 60 and 300 nanometers.

[0033] Especially preferred as the butadiene latex is a butadienepolymer that has been emulsion polymerized in the presence of a styrenesulfonic acid, styrene sulfonate, poly(styrene sulfonic acid), orpoly(styrene sulfonate) stabilizer to form the latex. Poly(styrenesulfonate) is the preferred stabilizer. This stabilization system isparticularly effective for a butadiene polymer that is derived from atleast 60 weight percent dichlorobutadiene monomer, based on the amountof total monomers used to form the butadiene polymer. The butadienepolymer latex can be made by known emulsion polymerization techniquesthat involve polymerizing the butadiene monomer (and copolymerizablemonomer, if present) in the presence of water and the styrene sulfonicacid, styrene sulfonate, poly(styrene sulfonic acid), or poly(styrenesulfonate) stabilizer. The sulfonates can be salts of any cationicgroups such as sodium, potassium or quaternary ammonium. Sodium styrenesulfonate is a preferred styrene sulfonate compound. Poly(styrenesulfonate) polymers include poly(styrene sulfonate) homopolymer andpoly(styrene sulfonate) copolymers such as those with maleic anhydride.Sodium salts of poly(styrene sulfonate) are particularly preferred andare commercially available from National Starch under the tradedesignation VERSA TL. The poly(styrene sulfonate) can have a weightaverage molecular weight from 5×10⁴ to 1.5×10⁶, with 1.5×10⁵ to 2.5×10⁵being preferred. In the case of a poly(styrene sulfonate) orpoly(styrene sulfonic acid) it is important to recognize that theemulsion polymerization takes place in the presence of the pre-formedpolymer. In other words, the butadiene monomer is contacted with thepre-formed poly(styrene sulfonate) or poly(styrene sulfonic acid). Thestabilizer preferably is present in an amount of 0.1 to 10 parts,preferably 1 to 5 parts, per 100 parts by weight of total monomersutilized to form the butadiene polymer.

[0034] The flexibilizer or film-former should be present in the adhesivein an amount of 5 to 60, preferably 20 to 30, weight percent, based onthe total dry weight of all the components of the adhesive.

[0035] The phenolic resin dispersion (B) is optional component, buttypically is present in the one coat adhesive embodiment. The phenolicresin dispersion (B) is disclosed in commonly assigned PCT PatentApplication Publication No. WO 99/37712, corresponding to U.S. patentapplication Ser. No. 09/235,777, filed Jan. 22, 1999, incorporatedherein by reference. The phenolic resin dispersion (B) of the inventivecomposition can be obtained by reacting or mixing a phenolic resinprecursor and a modifying agent—theoretically via a condensationreaction between the phenolic resin precursor and the modifying agent.

[0036] One functional moiety of the modifying agent provides the ionicpendant group that enables stable dispersion of the phenolic resin.Without the ionic pendant group, the phenolic resin would be unable tomaintain a stable dispersion in water. Since the ionic pendant groupprovides for the stability of the dispersion there is no need, or at themost a minimal need, for surfactants. The presence of surfactants in anaqueous composition is a well-known hindrance to the composition'sperformance.

[0037] The other important functional moiety in the modifying agentenables the modifying agent to react with the phenolic resin precursor.The modifying agent can contain more than one ionic pendant group andmore than one reaction-enabling moiety.

[0038] Incorporation of aromatic sulfonate functional moieties into thephenolic resin structure via condensation is the preferred method ofproviding the ionic pendant groups. Accordingly, one class of ionicmoieties is substituents on an aromatic ring that include a sulfur atomcovalently or ionically bonded to a carbon atom of the aromatic ring.Examples of covalently bound sulfur-containing substituents aresulfonate (—S(O)₂O⁻M⁺), sulfinate (—S(O)O⁻M⁺), sulfenate (—SO⁻M⁺) andoxysulfonate (—OS(O)₂O⁻M⁺), wherein M can be any monovalent ion such asNa, Li, K, or NR¹ ₃ (wherein R¹ is hydrogen or an alkyl). Anotherexample of a covalently bound substituent is sulfate ion. Sulfonate isthe preferred ionic group. The modifying agent should not include orintroduce any multivalent ions into the phenolic resin dispersion sinceit is expected that the presence of multivalent ions would cause thephenolic resin to precipitate rather than remain dispersed.

[0039] The reaction-enabling functional moiety of the modifying agentcan be any functional group that provides a site on the modifying agentfor undergoing condensation with a phenolic resin. If the phenolic resinprecursor is a resole, the modifying agent reacts with an alkylol orbenzyl ether group of the resole. If the modifying agent is aromatic,the reaction-enabling functional moiety is a substituent on the aromaticring that causes a site on the ring to be reactive to the alkylol orbenzyl ether of the resole precursor. Examples of such a substituent arehydroxy or hydroxyalkyl, with hydroxy being preferred. The hydroxy- orhydroxyalkyl-substituted aromatic modifying agent is reactive at a siteortho and/or para to each hydroxy or hydroxyalkyl substituent. In otherwords, the aromatic modifying agent is bonded to, or incorporated into,the phenolic resin precursor at sites on the aromatic ring of themodifying agent that are ortho and/or para to a hydroxy or hydroxyalkylsubstituent. At least two reaction-enabling functional moieties arepreferred to enhance the reactivity of the aromatic modifying agent withthe phenolic resin precursor.

[0040] Alternatively, the reaction-enabling functional moiety of themodifying agent can be a formyl group (—CHO), preferably attached to acarbon atom of an aromatic ring. In this instance, the phenolic resinprecursor is a novolak rather than a resole. The novolak precursor isreacted via an acid catalyzed aldehyde condensation reaction with theformyl group-containing modifying agent so that the formyl group forms adivalent methylene linkage to an active site on an aromatic ring of thebackbone structure of the novolak precursor. Consequently, the modifyingagent structure (including the ionic moiety) is incorporated into thephenolic structure through the generated methylene linkage. Examples ofsuch formyl group-containing modifying agents include 2-formylbenzenesulfonate, 5-formylfuran sulfonate and (R)(SO₃)CH—CH₂—C(O)(H) compoundswherein R is C₁-C₄ alkyl groups.

[0041] Another alternative reaction-enabling functional moiety could bea diazo group (—N₂ ⁺), preferably attached to a carbon atom of anaromatic ring. In this instance, the phenolic resin precursor is anovolak rather than a resole. The novolak precursor is reacted via adiazo coupling reaction with the diazo group-containing modifying agentso that the diazo group forms a divalent diazo linkage (—N═) to anactive site on an aromatic ring of the backbone structure of the novolakprecursor. Consequently, the modifying agent structure (including theionic moiety) is incorporated into the phenolic structure through thediazo linkage. An example of such a diazo modifying agent is1-diazo-2-naphthol-4-sulfonic acid.

[0042] The modifying agent also can optionally include a functionalmoiety that is capable of chelating with a metal ion that is present ona substrate surface on which the phenolic resin dispersion is applied.The chelating group remains as a residual group after the condensationof the phenolic resin precursor and the aromatic modifying agent.Typically, the chelating group is a substituent on the aromatic ringthat is capable of forming a 5- or 6-membered chelation structure with ametal ion. Examples of such substituents include hydroxy andhydroxyalkyl, with hydroxy being preferred. At least two such functionalgroups must be present on the modifying agent molecule to provide thechelating. In the case of an aromatic modifying agent, the chelatinggroups should be located in an ortho position relative to each other. Asignificant advantage of the invention is that hydroxy or hydroxyalkylsubstituents on the aromatic modifying agent can serve tworoles—condensation enablement and subsequent metal chelating.

[0043] An aromatic modifying agent is particularly advantageous.Preferably, the ionic group and the reaction-enabling moiety are notsubstituents on the same aromatic ring. The ionic group, particularlysulfonate, appears to have a strong deactivating effect on condensationreactions of the ring to which it is attached. Consequently, an ionicgroup attached to the same ring as the reaction-enabling moiety wouldnot allow the modifying agent to readily react with the phenolic resinprecursor. However, it should be recognized that this consideration forthe location of the ionic and reaction-enabling moieties is notapplicable to the formyl group-containing modifying agent and diazomodifying agent.

[0044] A preferred structure for the aromatic modifying agent isrepresented by formulae Ia or Ib below:

[0045] wherein X is the ionic group; Y is the reaction-enablingsubstituent; Z is the chelating substituent; L¹ is a divalent linkinggroup such as an alkylene radical (for example, methylene) or a diazo(—N═N—); a is 1; b is 1 to 4; m is 0 or 1; and c and d are eachindependently 0 to 3, provided there are not more than 4 substituents oneach aromatic ring. If a chelating group Z is present it is positionedortho to another chelating group Z or to Y. It should be recognized thatthe reaction-enabling substituent Y may also act as a chelatingsubstituent. In this instance, the aromatic modifying agent may notinclude an independent chelating substituent Z. An aromatic modifyingagent according to formulae Ia or Ib could also include othersubstituents provided they do not adversely interfere with the ionicgroup or the condensation reaction.

[0046] Illustrative aromatic modifying agents include salts of6,7-dihydroxy-2-napthalenesulfonate;6,7-dihydroxy-1-naphthalenesulfonate;6,7-dihydroxy-4-napthalenesulfonate; Acid Red 88; Acid Alizarin VioletN; Erichrome Black T; Erichrome Blue Black B; Brilliant Yellow; CroceinOrange G; Biebrich Yellow; and Palatine Chrome Black 6BN.6,7-dihydroxy-2-naphthalenesulfonate, sodium salt is the preferredaromatic modifying agent.

[0047] It should be recognized that the preferred sulfonate modificationcontemplated herein involves an indirect sulfonation mechanism. In otherwords, the aromatic modifying agent includes a sulfonate group and isreacted with another aromatic compound (the phenolic resin precursor) toobtain the chain extended, sulfonate-modified phenolic resin product.This indirect sulfonation is distinctly different than directsulfonation of the phenolic resin precursor.

[0048] Any phenolic resin could be employed as the phenolic resinprecursor, but it has been found that resoles are especially suitable.The resole precursor should have a sufficient amount of active alkylolor benzyl ether groups that can initially condense with the modifyingagent and then undergo further subsequent condensation. Of course, thephenolic resin precursor has a lower molecular weight than the finaldispersed resin since the precursor undergoes condensation to make thefinal dispersed resin. Resoles are prepared by reacting a phenoliccompound with an excess of an aldehyde in the presence of a basecatalyst. Resole resins are usually supplied and used as reactionproduct mixtures of monomeric phenolic compounds and higher molecularweight condensation products having alkylol (—ArCH₂—OH) or benzyl ethertermination (—ArCH₂—O—CH₂Ar), wherein Ar is an aryl group. These resolemixtures or prepolymers (also known as stage A resin) can be transformedinto three-dimensional, crosslinked, insoluble and infusible polymers bythe application of heat.

[0049] The reactants, conditions and catalysts for preparing resolessuitable for the resole precursor of the present invention are wellknown. The phenolic compound can be any of those previously listed orother similar compounds, although multi-hydroxy phenolic compounds areundesirable. Particularly preferred phenolic compounds for making theresole precursor include phenol per se and alkylated phenol. Thealdehyde also can be any of those previously listed or other similarcompounds, with formaldehyde being preferred. Low molecular weight,water soluble or partially water soluble resoles are preferred as theprecursor because such resoles maximize the ability to condense with themodifying agent. The F/P ratio of the resole precursor should be atleast 0.90. Illustrative commercially available resoles that aresuitable for use as a precursor include a partially water soluble resoleavailable from Georgia Pacific under the trade designation BRL 2741 anda partially water soluble resoles available from SchenectadyInternational under the trade designations HRJ11722 and SG3100.

[0050] As described above, the dispersed phenolic resin reaction productaccording to the invention can be hydrophilic or hydrophobic, buthydrophilic is preferred. In addition, dispersed resoles or novolaks canbe obtained depending upon the selection and amount of reactants.

[0051] Preferably, the dispersed resole is produced by reacting ormixing 1 mol of modifying agent(s) with 1 to 20 mol of phenolic resinprecursor(s). A dispersed resole typically can be obtained by reactingor mixing a resole precursor or a mixture of resole precursors with themodifying agent or a mixture of agents without any other reactants,additives or catalysts. However, other reactants, additives or catalystscan be used as desired. Multi-hydroxy phenolic compound(s) canoptionally be included in relatively small amounts in the reactantmixture for the resole.

[0052] Hydrophilic resoles typically have a F/P ratio of at least 1.0.According to the invention, hydrophilic resoles having a F/P ratio muchgreater than 1.0 can be successfully dispersed. For example, it ispossible to make an aqueous dispersion of hydrophilic resoles having aF/P ratio of at least 2 and approaching 3, which is the theoretical F/Pratio limit.

[0053] Preferably, the dispersed novolak is produced by reacting 1 molof modifying agent(s) with 2-20 mol of phenolic resin precursor(s) and,preferably, 2-20 mol of multi-hydroxy phenolic compound(s). An aldehydecompound, preferably formaldehyde, is also required to make the novolak.The aldehyde compound can optionally be added as a separate ingredientin the initial reaction mixture or the aldehyde compound can begenerated in situ from the resole precursor. The resole precursor(s),multi-hydroxy phenolic compound(s) and modifying agent(s) co-condense toform the dispersed novolak. The reaction typically is acid catalyzedwith an acid such as phosphoric acid. The F/P ratio of aldehydecompound(s) to combined amount of resole precursor(s) and multi-hydroxyphenolic compound(s) in the initial reaction mixture preferably is lessthan 0.9. Preferably, synthesis of the dispersed novolak is a two stagereaction. In the first stage, the resole precursor(s) is reacted withthe modifying agent(s) and, optionally, a small amount of multi-hydroxyphenolic compound(s). Once this first stage reaction has reached thedesired point (i.e. the resin can be readily formed into a translucentdispersion), the acid catalyst and a greater amount of multi-hydroxyphenolic compound(s) is added to the reaction mixture. Pyrocatechol(also simply known as catechol) is a preferred multi-hydroxy phenoliccompound for reacting in the first stage and resorcinol is a preferredmulti-hydroxy phenolic compound for reacting in the second stage.

[0054] Hydrophilic novolaks typically have a hydroxy equivalents ofbetween 1 and 3 per aromatic ring. Preferably, dispersed hydrophilicnovolaks according to the invention have a hydroxy equivalents of 1.1 to2.5, more preferably 1.1 to 2.0. The hydroxy equivalents is calculatedbased on the amount of multi-hydroxy phenolic compounds used to make thenovolak.

[0055] According to a preferred embodiment, the dispersed phenolic resinreaction product contains a mixture of oligomers having structuresbelieved to be represented by the following formulae IIa or IIb:

[0056] wherein X, Y, Z and L¹ and subscripts a, b, c, d and m are thesame as in formulae Ia and Ib, e is 1 to 6, L² is a divalent linkinggroup and Ph is the phenolic resin backbone structure, provided the-(L²-Ph) group(s) is(are) ortho or para to a Y group. L² depends uponthe particular phenolic resin, but typically is a divalent alkyleneradical such as methylene (—CH₂—) or oxydimethylene (—CH₂—O—CH₂—).Preferably, e is 2 and the -(L²-Ph) groups are in para position to eachother.

[0057] According to a particularly preferred embodiment wherein thephenolic resin is a resole and the modifying agent is a naphthalenehaving a ionic pendant group X and two reaction-enabling substituents Y,the dispersed phenolic resin reaction product contains a mixture ofoligomers having structures believed to be represented by the followingformula III:

[0058] wherein X and Y are the same as in formulae Ia and Ib, a is 0 or1; n is 0 to 5; R² is independently —C(R⁵)₂— or —C(R⁵)₂—O—C(R⁵)₂—,wherein R⁵ is independently hydrogen, alkylol, hydroxyl, alkyl, aryl oraryl ether; and R³ is independently alkylol, alkyl, aryl, alkylaryl oraryl ether. Preferably, R² is methylene or oxydimethylene and R³ ismethylol. If 6,7-dihydroxy-2-naphthalenesulfonate, sodium salt is themodifying agent, X will be SO₃ ⁻Na⁺ and each Y will be OH. It should berecognized that in this case the hydroxy groups for Y will also act aschelating groups with a metal ion.

[0059] According to another preferred embodiment wherein the phenolicresin is a novolak and the modifying agent is a naphthalene having aionic pendant group X and two reaction-enabling substituents Y, thedispersed phenolic resin reaction product contains a mixture ofoligomers having structures believed to be represented by the followingformula IV:

[0060] wherein X and Y are the same as in formulae Ia and Ib, a is 0 or1, n is 0 to 5 and R⁴ is independently hydroxyl, alkyl, aryl, alkylarylor aryl ether. Preferably, R⁴ is tert-butyl. If6,7-dihydroxy-2-naphthalenesulfonate, sodium salt is the modifyingagent, X will be SO₃ ⁻Na⁺ and each Y will be OH. In this case thehydroxy groups for Y will also act as chelating groups with a metal ion.

[0061] It should be recognized that the dispersed phenolic resinreaction product may contain oligomers or compounds having structuresthat vary from the idealized structures shown in formulae III and IV.

[0062] If the modifying agent includes a sulfur-containing ionic group,the resulting modified phenolic resin should have a carbon/sulfur atomratio of 20:1 to 200: 1, preferably 20:1 to 100:1. If the sulfur contentis greater than the 20:1 carbon/sulfur atom ratio, the modified phenolicresin begins to become water soluble, is more stable with respect tomultivalent ions and is difficult to thermoset. These characteristicsare adverse to the preferred use of the phenolic resin dispersion of theinvention. If the sulfur content is below the 200:1 carbon/sulfur atomratio, then the resin dispersion cannot maintain its stability. Viewedanother way, the dispersed phenolic resins have 0.01 to 0.10, preferably0.03 to 0.06, equivalents of sulfonate functionality/100 g resin. Theaqueous dispersion of the phenolic resin preferably has a solids contentof 1 to 50, preferably 15 to 30.

[0063] The modifying agent and the phenolic resin precursor can bereacted or mixed under conditions effective to promote condensation ofthe modifying agent with the phenolic resin precursor. The reaction iscarried out in water under standard phenolic resin condensationtechniques and conditions. The reactant mixture (including water)generally is heated from 50 to 100° C. under ambient pressure, althoughthe specific temperature may differ considerably depending upon thespecific reactants and the desired reaction product. The resultingproduct is a concentrate that is self-dispersible upon the addition ofwater and agitation to reach a desired solids content. The finaldispersion can be filtered to remove any gelled agglomerations.

[0064] The intermediate modified resoles or novolaks that are initiallyproduced in the synthesis are not necessarily water dispersible, but asthe chain extension is advanced the resulting chain extended modifiedresoles or novolaks become progressively more water dispersible bysimple mechanical agitation. The chain extension for the dispersedresole is determined by measuring the viscosity of the reaction mixture.Once the resole reaction mixture has a reached the desired viscosity,which varies depending upon the reactant composition, the reaction isstopped by removing the heat. The chain extension for the dispersednovolak is determined by pre-selecting the F/P ratio of the totalreaction mixture (in other words, the amount of aldehyde compound(s)relative to the amount of phenolic(s) in both the first and secondstages). The reaction for the novolak is allowed to proceed untilsubstantially all of the total amount of the reactants have reacted. Inother words, there is essentially no unreacted reactant remaining.Preferably, the molecular weight (i.e., chain extension) of both theresole and novolak should be advanced to just below the gel point.

[0065] The phenolic resin dispersion can be present in the compositionof the invention in an amount of 5 to 75 weight percent based on thetotal dry weight of the composition. Preferably, the phenolic resindispersion is present in the control agent-containing one coatembodiment in an amount of 40 to 60 weight percent, based on the totaldry weight of the composition. Preferably, the phenolic resin dispersionis present in the crosslinker-containing one coat embodiment in anamount of 5 to 20 weight percent, based on the total dry weight of thecomposition.

[0066] The acid (C) can be any acid that is capable of adjusting the pHof the adhesive composition to 1-3. Illustrative acids includehydrofluoric acid, phosphoric acid, sulfuric acid, hydrochloric acid andnitric acid. Aqueous solutions of phosphoric acid are preferred. Whenthe acid is mixed into the composition presumably the respective ionsare formed and exist as independent species in addition to the presenceof the free acid. In other words, in the case of phosphoric acid,phosphate ions and free phosphoric acid co-exist in the formulated finalmulti-component composition. The acid preferably is present in an amountof 5 to 300 parts by weight, more preferably 10 to 160 parts by weight,based on 100 parts by weight of the phenolic novolak resin dispersion(B). The covercoat embodiment preferably does not include an acid.

[0067] Water, preferably deionized water, is utilized in the adhesivecomposition of the invention in order to vary the solids content and toprovide a carrier fluid for mixing the ingredients of the adhesive anddelivering the adhesive to a substrate surface. Since the adhesivecomposition is waterborne, it is substantially free of volatile organiccompounds.

[0068] According to one embodiment of the one coat adhesive, there isincluded a control agent that improves the uniformity of the filmthickness formed by the adhesive. The control agent may be a nitrocompound, a nitroso compound, an oxime compound, a nitrate compound, ora similar material. A mixture of control agents may be used. Organicnitro compounds are the preferred control agents.

[0069] The organic nitro compound is any material that includes a nitrogroup (—NO₂) bonded to an organic moiety. Preferably, the organic nitrocompound is water soluble or, if water insoluble, capable of beingdispersed in water. Illustrative organic nitro compounds includenitroguanidine; aromatic nitrosulfonates such as nitro ordinitrobenzenesulfonate and the salts thereof such as sodium, potassium,amine or any monovalent metal ion (particularly the sodium salt of3,5-dinitrobenzenesulfonate); Naphthol Yellow S; and picric acid (alsoknown as trinitrophenol). Especially preferred for commercialavailability and regulatory reasons is a mixture of nitroguanidine andsodium nitrobenzenesulfonate.

[0070] The amount of control agent(s) in the adhesive composition mayvary, particularly depending upon the amount of any acid in thecomposition. Preferably, the amount is up to 20 weight %, morepreferably up to 10 weight %, and most preferably 2 to 5 weight %, basedon the total amount of non-volatile ingredients in the adhesivecomposition. According to a preferred embodiment, the weight ratio ofnitroguanidine to sodium nitrobenzenesulfonate should range from 1:10 to5:1.

[0071] The organic nitro compound typically is mixed into thecomposition in the form of an aqueous solution or dispersion. Forexample, nitroguanidine is a solid at room temperature and is dissolvedin water prior to formulating into the composition.

[0072] A crosslinker is useful in an embodiment of the one coat adhesiveand in the covercoat adhesive. The crosslinker can be an aromaticnitroso compound or aromatic nitroso compound precursor. The aromaticnitroso compound can be any aromatic hydrocarbon, such as benzenes,naphthalenes, anthracenes, biphenyls, and the like, containing at leasttwo nitroso groups attached directly to non-adjacent ring carbon atoms.Such aromatic nitroso compounds are described, for example, in U.S. Pat.No. 3,258,388; U.S. Pat. No. 4,119,587 and U.S. Pat. No. 5,496,884. Thearomatic nitroso compound or aromatic nitroso compound precursor, ifpresent, is preferably in an amount of 5 to 60, more preferably 20 to30, weight percent, based on the total dry weight of the adhesive. Anaromatic nitroso compound precursor is preferred.

[0073] More particularly, such nitroso compounds are described asaromatic compounds having from 1 to 3 aromatic nuclei, including fusedaromatic nuclei, having from 2 to 6 nitroso groups attached directly tonon-adjacent nuclear carbon atoms. The preferred nitroso compounds arethe dinitroso aromatic compounds, especially the dinitrosobenzenes anddinitrosonaphthalenes, such as the meta- or para-dinitrosobenzenes andthe meta- or para-dinitrosonaphthalenes. The nuclear hydrogen atoms ofthe aromatic nucleus can be replaced by alkyl, alkoxy, cycloalkyl, aryl,aralkyl, alkaryl, arylamine, arylnitroso, amino, halogen and similargroups. Thus, where reference is made herein to “aromatic nitrosocompound” it will be understood to include both substituted andunsubstituted nitroso compounds.

[0074] Particularly preferred nitroso compounds are characterized by theformula:

(R)_(m)—Ar—(NO)₂

[0075] wherein Ar is selected from the group consisting of phenylene andnaphthalene; R is a monovalent organic radical selected from the groupconsisting of alkyl, cycloalkyl, aryl, aralkyl, alkaryl, arylamine andalkoxy radicals having from 1 to 20 carbon atoms, amino, or halogen, andis preferably an alkyl group having from 1 to 8 carbon atoms; and m is0, 1, 2, 3, or 4, and preferably is 0.

[0076] Exemplary suitable aromatic nitroso compounds includem-dinitrosobenzene, p-dinitrosobenzene, m-dinitrosonaphthalene,p-dinitrosonaphthalene, 2,5-dinitroso-p-cymene,2-methyl-1,4-dinitrosobenzene, 2-methyl-5-chloro-1,4-dinitrosobenzene,2-fluoro-1,4-dinitrosobenzene, 2-methoxy-1-3-dinitrosobenzene,5-chloro-1,3-dinitrosobenzene, 2-benzyl-1,4-dinitrosobenzene,2-cyclohexyl-1,4-dinitrosobenzene and combinations thereof. Particularlypreferred are m-dinitrosobenzene and p-dinitrosobenzene.

[0077] The aromatic nitroso compound precursor may be essentially anycompound that is capable of being converted, typically by oxidation, toa nitroso compound at elevated temperatures, typically from about140-200° C. This conversion usually occurs during the bonding procedureused with the adhesive. The most common aromatic nitroso compoundprecursors are quinone compounds. Examples of such quinone compoundsinclude quinone dioxime, dibenzoquinone dioxime,1,2,4,5-tetrachlorobenzoquinone, 2-methyl-1,4-benzoquinone dioxime,1,4-naphthoquinone dioxime, 1,2-naphthoquinone dioxime and2,6-naphthoquinone dioxime. Quinone dioxime is especially preferred.

[0078] Additional ingredients can be included in the adhesivecomposition. Such ingredients include metal oxides, inert fillers,polymeric film-forming adjuncts, surfactants, dispersing agents, wettingagents, pigments, carbon black, silica and the like.

[0079] The compositions may be prepared by any method known in the art,but are preferably prepared by combining and milling or shaking theingredients and water in ball-mill, sand-mill, ceramic bead-mill,steel-bead mill, high speed media-mill or the like. It is preferred toadd each component to the mixture in a liquid form such as an aqueousdispersion, emulsion or latex.

[0080] The composition is applied to a substrate surface by dipping thesubstrate or part into a bath of the composition. Typically, the metalsubstrate is dipped into the bath. The metal substrate can reside in theadhesive composition bath for an amount of time sufficient to deposit auniform film of desired thickness. Typically, the bath residence time isfrom about 5 to about 120 seconds, preferably about 10 to about 30seconds, and occurs at room temperature. The composition typically isapplied to form a dry film thickness of 10 to 30 μm.

[0081] According to the present invention when the composition isapplied to an electrochemically active metal surface under conditionsthat generate multivalent ions on the surface the multivalent ionsappear to cause the composition to deposit on the metal surface asubstantially self-limiting, substantially uniform, gelatinous, wetfilm. The coating that is formed when the composition is in contact withthe metal surface is known as the “uncured” state. The subsequent dryingof the coating converts the coating to a “cured” stage. The formation ofthe coating is “self-limiting” in that the coating occurs rapidlyinitially and then the deposition rate rapidly decreases thus limitingthe thickness and area density (mass per unit area) with time.

[0082] In the case of the one coat adhesive embodiment the metal surfaceactivation typically is initiated by the acid that is present in the onecoat adhesive composition. In the case of the covercoat adhesiveembodiment the metal surface can be activated by the prior applicationof an autodepositable metal treatment composition that includes anappropriate acid or a primer that includes an appropriate acid. Suchmetal treatment compositions and primers are respectively described, forexample, in commonly assigned PCT Patent Publication No. WO 99/37722corresponding to U.S. patent application Ser. No. 09/235,201, filed Jan.22, 1999, incorporated herein by reference, and commonly assigned PCTPatent Publication No. WO 99/37713 corresponding to U.S. patentapplication Ser. No. 09/235,778, filed Jan. 22, 1999, incorporatedherein by reference.

[0083] The adhesive composition can be used to bond any types ofadherends together, but it is particularly useful to bond a metalsurface to a polymeric material surface. The polymeric material can beany elastomeric material selected from any of the natural rubbers andolefinic synthetic rubbers including polychloroprene, polybutadiene,neoprene, styrene-butadiene copolymer rubber, acrylonitrile-butadienecopolymer rubber, ethylene-propylene copolymer rubber (EPM),ethylene-propylene-diene terpolymer rubber (EPDM), butyl rubber,brominated butyl rubber, alkylated chlorosulfonated polyethylene and thelike. The material may also be a thermoplastic elastomer such as thosesold under the trade designations SANTOPRENE and ALCRYN by Monsanto andDuPont, respectively. The metal surface may be selected from any of thecommon structural metals such as iron, steel (including stainless steeland electrogalvanized steel), lead, aluminum, copper, brass, bronze,MONEL metal alloy, nickel, zinc and the like.

[0084] For adhesive bonding, the adhesive composition typically isapplied to the metal surface and then dried. The coated metal surfaceand elastomeric surface are brought together under heat and pressure tocomplete the bonding procedure. The exact conditions selected willdepend upon the particular elastomer being bonded and whether or not itis cured prior to bonding. In some cases, it may be desirable to heatthe metal surface prior to application of the primer and/or covercoatcomposition(s) to assist in drying of the composition(s). The coatedmetal surface and the elastomeric surface are typically brought togetherunder a pressure of 20 to 175 MPa, preferably from 20 to 50 MPa. If theelastomer is uncured, the resulting elastomer-metal assembly issimultaneously heated to a temperature of 140° C. to 220° C., preferably160° C. to 200° C. The assembly should remain under the applied pressureand temperature for a period of 1 minute to 60 minutes, depending on thecure rate and thickness of the elastomeric substrate. If the elastomeris already cured, the bonding temperature may range from 90° C. to above180° C. for 15 to 120 minutes.

[0085] The bonding process may be carried out by introducing theelastomer as a semi-molten material to the metal surface as in, forexample, an injection-molding process. The process may also be carriedout by utilizing compression molding, transfer molding or autoclavecuring techniques. After the process is complete, the bond is fullyvulcanized and ready for use in a final application.

[0086] One composition that is particularly useful as a one coatadhesive for bonding nitrile rubber to a metal substrate, especiallysteel, includes a flexibilizer (A), the novolak embodiment of thephenolic resin dispersion (B), an acid (C) and a control agent.

[0087] The invention will be described in more detail by way of thefollowing non-limiting examples. The failure mechanism for the testedbond is expressed in terms of percent. A high percent of rubber retained(R) on the metal coupon is desirable since this indicates that theadhesive bond is stronger than the rubber itself. Rubber-cement failure(RC) indicates the percentage of failure at the interface between therubber and the adhesive. Cement-metal failure (CM) indicates thepercentage of failure at the interface between the metal substrate andthe adhesive.

[0088] For the boiling water test the bonded test assemblies or couponswere prepared according to ASTM-D-429-B. The leading edge of each of theassemblies was stressed by suspending a two kg weight on the overlappingrubber tail and the assembly was then mounted in a fixture so that therubber tail was at an approximately 90° angle to the plane formed by thebonded interface. The stressed edge interface was exposed to boilingwater by immersing the coupon in boiling water for the indicated timeperiod. After this time, the coupons were removed from the boilingwater, allowed to cool and tested on either an Instron mechanical testerby pulling the rubber off the metal at a 45° angle stripping fixturewith a crosshead speed of 2 inches per minute or by manually peeling therubber from the metal substrate. The amount of rubber retained on thebonded area is recorded as a percentage as described above.

[0089] For the salt spray test the bonded test assemblies preparedaccording to ASTM-D-429-B were buffed on the edges with a grindingwheel. The rubber is then tied back over the metal with stainless steelwire so as to stress the bonded area. This exposes the bond line to theenvironment. The assemblies then are strung on stainless steel wire andplaced in a salt spray chamber. The environment inside the chamber is100° F., 100 percent relative humidity and 5 percent dissolved salt inthe spray, which is dispersed throughout the chamber. The assembliesremain in this environment for the indicated time period. Upon removal,the rubber is peeled manually from the metal substrate. The amount ofrubber retained on the bonded area is recorded as a percentage asdescribed above.

EXAMPLES 1-2 Bonding with Autodepositable One Coat Adhesive

[0090] A dispersed novolak resin was made by mixing 200 g of resorcinol,20 g of pyrogallol, 12 g of phosphoric acid (855 aqueous solution) and220 g of water together and heating to 95° C. When 95° C. was reached,250 g of formalin (18.5% aqueous solution) was fed to the reactionmixture over a period of 30 minutes. Steam heating was continued foranother 15 minutes at which point the mixture was slightly turbid andhad a low viscosity (a sample precipitated out of solution upon dilutionwith water). 16 g of 2-formylbenzenesulfonic acid (sodium salt, 75%moist solid) and 40 more g of foimalin then were added. After one hourand 15 minutes of steam heating the resin was very viscous. 200 g ofwater were added and heating continued for another 15 minutes. Eightmore g of formalin were added and heating continued for another 30minutes. 580 g of water was added to the resin mixture and steam heatingwas continued until the resin was completely dispersible.

[0091] This dispersed resin was mixed into a composition (Example 1)with the following ingredients in wet weight amounts: 37.5 g novolakdispersion; 37.5 g phosphoric acid; 85 g water; 15 g dinitrobenzenesulfonate; and 11.25 g dichlorobutadiene homopolymer latex.

[0092] Another dispersed novolak resin was made as described aboveexcept that 32 g of the 2-formylbenzenesulfonic acid was used. Thisdispersed resin was mixed into a composition (Example 2) with thefollowing ingredients in wet weight amounts: 37.5 g novolak dispersion;37.5 g phosphoric acid; 85 g water; 15 g dinitrobenzene sulfonate; and11.25 g dichlorobutadiene homopolymer latex.

[0093] One set of cold rolled steel coupons was dipped for 10 seconds ina bath of the Example 1 composition and another set of cold rolled steelcoupons were dipped for 10 seconds in a bath of the Example 2composition. The coated coupons were dried at 180° F.

[0094] Different peroxide-cured and sulfur-cured nitrile rubbersubstrates were bonded to the coated steel coupons at by applying heatof 375 to 400° F. for 2 to 3 minutes. Primary adhesion of the resultingassemblies was tested according to ASTM 429 B and the result indicatedin Table 1 in units of lb(f)/in. The failure mode for each bondedassembly is also shown in Table 1. TABLE 1 Example 1 Example 2 NitrileRubber Lb Failure mode Lb Failure mode Peroxide-cured-1 21 5R, 95RC 2218R, 83RC Peroxide-cured-2 43 58R, 23RC, 20MT* 34 38R, 63RCSulfur-cured-1 18 100RC 22 100RC Sulfur-cured-2 35 100RC 32 100RCPeroxide-cured-3 38 40R, 8RC, 50MT 52 65R, 35RC Peroxide-cured-4 39 20R,35RC, 45MT 49 100R Peroxide-cured-5 5 63RC, 38MT 5 100RCPeroxide-cured-6 5 100RC 5 100RC

EXAMPLE 3 Bonding with Autodepositable Covercoat

[0095] A phenolic novolak resin aqueous dispersion was made by mixingtogether 160 g of sodium salt of 6,7-dihydroxy-2-naphthalenesulfonate,544 g of a water soluble resole (made from formaldehyde and phenol, F/Pratio of 2.3, 80% solids and commercially available from Schenectadyunder the trade designation HRJ11722), 200 g of catechol and 200 g ofwater and steam heating for approximately two hours until the reactionmixture became very viscous and provided a clear dispersion. 880 g ofresorcinol and 500 g of water were added followed by 12 g of phosphoricacid in 10 g of water. Steam heating was continued for another 15minutes. 640 g of formalin (18.5% aqueous solution) then was added whilecontinuing steam heating resulting in a resin concentrate. Theconcentrate was filtered and self-dispersed upon the addition of 5900 gof water. This novolak dispersion was used to make an autodepositablemetal treatment composition by mixing the following ingredients in wetweight amounts: 180 g of the novolak dispersion (20% solids); 180 gphosphoric acid (10% solids); 475 g water; 76 g 2,4-dinitrobenzenesulfonate (5% solids); and 36 g of HYCAR 1578 latex (50% solids).

[0096] A phenolic resole resin aqueous dispersion was made by mixingtogether 40 g of sodium salt of 6,7-dihydroxy-2-naphthalenesulfonate,250 g of the HRJ11722 resole resin, and 50 g of water and steam heatingfor approximately 2 hours until the reaction mixture became very viscousand provided a transparent dispersion. 800 g of water was added to theresulting resin concentrate which then self-dispersed and was filtered.This resole dispersion was used to make an autodepositable adhesivecovercoat having a solids content of 15% by mixing together thefollowing ingredients in wet weight amounts: 18 g carbon black; 60 gzinc oxide; 75 g mica; 360 g aqueous phenolic resole resin dispersion;540 g phenolic resole aqueous dispersion that incorporates a non-ionicprotective colloid, presumably polyvinyl alcohol, (available fromGeorgia-Pacific under the trade designation GP 4000); 600 gdichlorobutadiene homopolymer latex; and 2800 g water.

[0097] Cold rolled steel coupons were dipped into a bath of the metaltreatment composition at room temperature for 15 seconds. After removalfrom the metal treatment bath, the treated coupons were dried at 180° F.for 3-5 minutes resulting in the formation of an autodeposited film. Thetreated metal coupons then were dipped for 10 seconds in a bath of thecoating/primer. After removal from the coating/primer bath, the couponswere dried at 180° F. for 5-10 minutes. One set of the coupons then washeated for five minutes at 325° F., another set of the coupons washeated for 15 minutes at 320° F. Peroxide-cured nitrile rubber then wasbonded to the treated and primed coupons via compression molding at 400°F. for 2 minutes.

[0098] The resulting bonded assemblies were tested for primary adhesionby ASTM 429 B. The results for the five minute-baked assemblies was abonding performance of 100% R and a bond strength of 38 lb(f)/in and forthe fifteen minute-baked assemblies was a bonding performance of 100% Rand a bond strength of 40 lb(f)/in.

EXAMPLE 4 Bonding with Autodepositable One Coat Adhesive

[0099] An autodepositable one coat adhesive was made by mixing togetherthe following ingredients in amounts of dry parts by weight (pbw): 40pbw dinitrosobenzene; 5 pbw silica (available from Cabot under thetradename CABOSWL); 10 pbw polymaleimide (available from Mitsui ToatsuFine Chemicals under the tradename BMI-M-20); 1 pbw surfactant (POLYWET1766); 15 pbw titanium dioxide; and 28 pbw dichlorobutadiene homopolymerto form a masterbatch. Phosphoric acid then was mixed into themasterbatch to reduce the pH to 2. Zinc phosphatized steel coupons thenwere dipped into the resulting composition. Upon removal of the coupons,a dry film of 0.6 mils uniform thickness was formed indicatingsuccessful autodeposition. After drying of the film, natural rubber wasbonded to the adhesive-coated coupons for 16 minutes at 320° F. viacompression molding. The resulting bonded assemblies then were testedfor primary adhesion, 2 hour boiling water test and 200 hour salt spraytest with results of 100% R for primary adhesion; 55% R,45% RC forboiling water; and 95% R, 5% RC for salt spray.

[0100] Another composition based on the above formulation was made byadding 10 weight percent dispersed phenolic resin after the phosphoricacid. The dispersed phenolic resin was the same as that described inExample 3. Zinc phosphatized steel coupons then were dipped into theresulting composition. Upon removal of the coupons, a dry film of 0.36mils uniform thickness was formed indicating successful autodeposition.After drying of the film, natural rubber was bonded to theadhesive-coated coupons for 16 minutes at 320° F. via compressionmolding. The resulting bonded assemblies then were tested for primaryadhesion, 2 hour boiling water test and 200 hour salt spray test withresults of 100% R for primary adhesion; 100% R for boiling water; and100% R for salt spray.

We claim:
 1. An aqueous adhesive comprising a mixture of at least oneflexibilizer ingredient wherein the adhesive is capable ofautodepositing on a metal substrate.
 2. An adhesive according to claim 1wherein the flexibilizer comprises a polymer selected from a halogenatedpolyolefin, an acrylonitrile-butadiene rubber or a styrene-acrylicpolymer.
 3. An adhesive according to claim 1 wherein the adhesive is aone coat adhesive and further comprises at least one acid selected fromhydrofluoric acid, phosphoric acid, sulfuric acid, hydrochloric acid ornitric acid.
 4. An adhesive according to claim 3 wherein the acidcomprises phosphoric acid.
 5. An adhesive according to claim 1 furthercomprising an aqueous phenolic resin dispersion ingredient.
 6. Anadhesive according to claim 1 wherein the adhesive is a covercoatadhesive and further comprises at least one crosslinker selected from anaromatic nitroso compound or aromatic nitroso compound precursor.
 7. Anadhesive according to claim 3 wherein the adhesive further comprises atleast one crosslinker selected from an aromatic nitroso compound oraromatic nitroso compound precursor.
 8. An adhesive according to claim 3wherein the adhesive further comprises at least one control agentselected from a nitro compound, a nitroso compound, an oxime compound ora nitrate compound.
 9. An adhesive according to claim 1 wherein theflexibilizer is selected from (poly)butadiene, neoprene,styrene-butadiene rubber, acrylonitrile-butadiene rubber, halogenatedpolyolefin, acrylic polymer, urethane polymer, ethylene-propylenecopolymer rubber, ethylene-propylene-diene terpolymer rubber,styrene-acrylic copolymer, polyamide or poly(vinyl acetate).
 10. Anadhesive according to claim 6 wherein the flexibilizer is selected froma halogenated polyolefin, an acrylonitrile-butadiene rubber or astyrene-acrylic polymer.
 11. An adhesive according to claim 6 furthercomprising an aqueous phenolic resin dispersion ingredient.
 12. Anadhesive according to claim 7 further comprising an aqueous phenolicresin dispersion ingredient.
 13. An adhesive according to claim 8further comprising an aqueous phenolic resin dispersion ingredient. 14.A method for bonding together two substrates comprising autodepositingan adhesive composition onto at least one of the substrates, wherein theadhesive composition comprises at least one flexibilizer ingredient. 15.A method according to claim 14 wherein one of the substrates is anelastomeric material and the other substrate is a metallic material andthe adhesive composition is autodeposited on the metallic substrate. 16.A method according to claim 15 further comprising applying a primer ormetal treatment to the metallic substrate and then autodepositing theadhesive composition over the primer or metal treatment.
 17. A methodaccording to claim 15 wherein an adhesive primer is not applied to themetallic substrate prior to autodepositing the adhesive composition. 18.A method according to claim 14 wherein the flexibilizer comprises apolymer selected from a halogenated polyolefin, anacrylonitrile-butadiene rubber or a styrene-acrylic polymer.
 19. Amethod according to claim 17 wherein the adhesive composition furthercomprises at least one acid selected from hydrofluoric acid, phosphoricacid, sulfuric acid, hydrochloric acid or nitric acid.
 20. A methodaccording to claim 19 wherein the acid comprises phosphoric acid.
 21. Amethod according to claim 14 wherein the adhesive composition furthercomprises an aqueous phenolic resin dispersion ingredient.
 22. A methodaccording to claim 14 wherein the adhesive composition comprises waterand is substantially free of volatile organic compounds.
 23. A methodaccording to claim 17 wherein the adhesive composition further comprisesa control agent ingredient that improves the thickness uniformity of thefilm formed by the adhesive.
 24. A method according to claim 15comprising dipping the metallic substrate into the adhesive compositionto effect autodeposition of the adhesive composition.
 25. A methodaccording to claim 24 wherein the dipping is performed at roomtemperature.
 26. A method for bonding a bonding a nitrile rubbersubstrate to a metallic substrate comprising autodepositing an adhesivecomposition onto the metallic substrate, wherein the adhesivecomposition comprises a mixture of at least one flexibilizer ingredient,an aqueous novolak dispersion ingredient, at least one acid ingredientand at least one control agent ingredient that improves the thicknessuniformity of the film formed by the adhesive.
 27. A method according toclaim 26 wherein an adhesive primer is not applied to the metallicsubstrate prior to autodepositing the adhesive composition.
 28. Anarticle of manufacture comprising a metallic substrate adhesively bondedto a metallic substrate wherein the substrates were bonded by the methodof claim
 14. 29. A method according to claim 16 wherein the adhesivecomposition further comprises at least one crosslinker selected from anaromatic nitroso compound or aromatic nitroso compound precursor.
 30. Amethod according to claim 29 wherein the adhesive further comprises anaqueous phenolic resin dispersion.
 31. A method according to claim 19wherein the adhesive further comprises at least one control agentselected from a nitro compound, a nitroso compound, an oxime compound ora nitrate compound.
 32. A method according to claim 19 wherein theadhesive composition further comprises at least one crosslinker selectedfrom an aromatic nitroso compound or aromatic nitroso compoundprecursor.
 33. A method according to claim 31 wherein the adhesivefurther comprises an aqueous phenolic resin dispersion.
 34. A methodaccording to claim 32 wherein the adhesive further comprises an aqueousphenolic resin dispersion.